The goal of this proposal is to determine the role of the developing salivary immune response to colonization of mucosal surfaces by selected commensal oral bacteria. The normal oral flora comprises many bacterial species, some are pathogenic producing diseases ranging from chronic low-grade infection of tooth and periodontium, to acute, systemic, life-threatening sepsis, meningitis and pneumonia. Although the salivary immune system recognizes and responds to oral bacteria the extent to which it plays a role in the regulation of the indigenous oral flora is unclear. An understanding of the mechanisms by which host protection is mediated against commensal bacteria with pathogenic potential is essential to the development of vaccines for their control. The objective of this proposal is to determine the relationship between the levels, isotypes and specificities of salivary antibodies and the colonization of selected oral bacteria. The bacteria chosen for study are Streptococcus mutans, S. agalactiae (GBS), Actinomyces viscosus, A. naeslundii and Bacteroides intermedius. These bacteria were selected because they have been implicated in chronic low-grade infection (dental caries and periodontitis) or severe acute sepsis and they represent genera that are either unique to the mouth or are oral species of genera that predominate at other mucosal surfaces. It is proposed to conduct a longitudinal study in infants from birth to age two years. The specific aims of this study are to (1) determine the kinetics of colonization of S. mutans, A. viscosus, A. naeslundii, B. intermedius and GBS using selective media and fluorescent antibodies, (2) determine the levels and isotypes of salivary antibodies induced in response to colonization of the selected bacteria using an enzyme-linked immunosorbent assay (ELISA) (3) determine the specificity of antibodies induced in response to colonization by Western blotting (4) identify and characterize immunodominant surface antigens using monoclonal antibodies and high performance liquid chromatography and (5) correlate the levels, isotypes and specificity of salivary antibodies with colonization of the selected bacteria by comparing ELISA titers and Western blot profiles with the appearance and number of the selected bacteria in the mouth. As immunity in the neonate's oral cavity may be influenced by maternal transfer of antibody in breast milk and through the placenta, the effect of passive immunity on colonization of the selected bacteria will also be addressed in Specific Aims 2-5.